Bond enthalpy, or bond dissociation energy, is crucial for understanding the energy required to break chemical bonds in molecules, particularly in gaseous substances. It indicates bond stability and is pivotal in calculating reaction enthalpies, using mean bond enthalpies or Hess's Law. This concept is also key in analyzing trends in combustion enthalpies across homologous series, such as alcohols, and requires adjustments for phase changes in reactions.
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Bond enthalpy is the energy required to break a chemical bond in one mole of a gaseous substance
Symbol ΔH°
Bond enthalpy is represented by the symbol ΔH°, with the specific bond indicated in brackets
Calculation Assumptions
Bond enthalpy calculations are based on the assumption that all reactants and products are in the gas phase
Mean bond enthalpies are average values that represent the typical energy required to break a specific type of bond in a range of compounds
Bond enthalpy values are essential for predicting the energetics of reactions
Hess's Law allows for the calculation of the enthalpy change for a reaction by using bond enthalpies
Bond enthalpy calculations can be used to determine the enthalpy change of a reaction by subtracting the total bond enthalpies of the bonds formed from the total bond enthalpies of the bonds broken
The enthalpy of vaporisation must be included in bond enthalpy calculations for reactions involving liquids
Adjustments are necessary for bond enthalpy calculations involving liquids or solids
Bond enthalpy calculations can be used to analyze trends in the enthalpies of combustion within a homologous series
Bond enthalpy calculations can be used to predict enthalpies of combustion for members of a homologous series with greater accuracy than experimental calorimetry
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Definition of Bond Enthalpy
Energy needed to break a chemical bond in 1 mole of a gaseous substance, leading to separate atoms.
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Symbol Representing Bond Enthalpy
ΔH°, with the specific bond shown in brackets (e.g., ΔH°(H-H)).
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Bond Enthalpy Assumption for Reactants and Products
Assumes all reactants and products are in the gas phase for calculation.
